a review of corrosion and protection of steel in … papers/paper 58.pdf · corrosion and stress...
Post on 25-May-2020
2 Views
Preview:
TRANSCRIPT
1
A REVIEW OF CORROSION AND PROTECTION OF STEEL IN CONCRETE
Arpit Goyal
PhD scholar, Centre of Built and Natural Environment, Coventry University, Coventry, CV1 2HF, United Kingdom, Email:
goyala4@uni.coventry.ac.uk, Mob: +447469308082
Homayoon Sadeghi Pouya
Research fellow, School of Energy, Construction and Environment, Sir John Laing Building, Coventry University, Coventry, CV1 2HF,
United Kingdom
Eshmaiel Ganjian
Professor, School of Energy, Construction and Environment, Built & Natural Environment Research Centre, Coventry University, Coventry,
CV1 2JH, United Kingdom
Peter Claisse
Emeritus Professor, School of Energy, Construction and Environment, Sir John Laing Building, Coventry University, Coventry, CV1 2HF,
United Kingdom
Abstract
Corrosion of reinforcement is one of the
major durability challenges which leads to
a reduction in the design life of reinforced
concrete. Due to an increasing demand for
longer service lives of infrastructure
(typically 100-120 years) and the high cost
involved in building and maintaining it, the
repair of concrete structures has become
extremely important. This paper discusses
mechanism of corrosion in reinforced
concrete and its thermodynamic and kinetic
behaviour. It also presents and compares
different corrosion prevention and
protection techniques available and
recommended by BS 1504-9:2008;
including the use of corrosion inhibitors,
alternative reinforcement, steel and
concrete coating and electrochemical
techniques. It is concluded that the
electrochemical techniques are more
effective than conventional methods.
2
Keywords: Reinforcement Corrosion,
Electrochemical Techniques, Corrosion
Protection, Corrosion Inhibitors,
Alternative Reinforcement, Coating
1 Introduction
Durability issues associated with concrete
structures are some of the biggest problems
the civil engineering community is facing
today around the world. One of the most
significant durability issues is the corrosion
of steel reinforcement, which leads to rust
formation, cracking, spalling, delamination
and degradation of structures. This is
considered to be the main factor causing
damage in bridges and other infrastructure
[1, 2]. Atmospheric corrosion, galvanic
corrosion and stress corrosion cracking can
impact the performance and appearance of
concrete structures. Therefore, to deal with
these issues, research around the globe is
oriented towards developing methods or
materials to prevent this corrosion of steel
in concrete. This paper presents a review of
reinforcement corrosion, its mechanisms,
and prevention.
2 Corrosion of Steel in Concrete
In general, when metals and alloys interact
with their environment chemically,
biochemically or electrochemically, surface
loss occurs, and they convert to their
oxides, hydroxides, or carbonates which are
more thermodynamically stable. This
process is termed as corrosion [1].
Along the surface of an embedded steel bar,
when there is a difference in electrical
potential, the concrete acts as an
electrochemical cell which consists of
anodic and cathodic regions on the steel,
with the pore water in the hardened cement
paste acting as an electrolyte [3]. This
generates a flow of current through the
system, causing an attack on the metal with
the more negative electrode potential i.e.
the anode while the cathode remains
undamaged [4]. Thus, corrosion of rebar is
initiated.
3
2.1 Mechanism of Corrosion of Steel in
Concrete
As soon as the hydration of cement starts,
steel in concrete develops a protective
passive layer on its surface which consists
adhering tightly to the steel 3O2Fe-ɣof
1-10to 3–10 of in the range sthicknes ith aw
µm [5]. This layer, blocks the movement
of ions between the steel and surrounding
concrete; thereby reducing the corrosion
rate [6]. The presence of this oxide layer
prevents damage of steel. It is only stable
at high pH i.e. 12-14 [1, 3]. For corrosion
to take place, this layer must be broken
down. This occurs in presence of
carbonation or chloride ions or poor
quality concrete, and, in the presence of
water and oxygen, corrosion occurs [7].
The process of corrosion can be understood
through Fig. 1 and equations. 1-5 [8]:
Anodic Reaction
𝐹𝑒 → 𝐹𝑒2+ + 2𝑒− (1)
𝐹𝑒2+ + 2𝑂𝐻− → 𝐹𝑒(𝑂𝐻)2 (2)
(Ferrous hydroxide)
4𝐹𝑒(𝑂𝐻)2 + 2𝐻2𝑂 + 𝑂2 → 4𝐹𝑒(𝑂𝐻)3 (3)
(Ferric hydroxide)
2𝐹𝑒(𝑂𝐻)3 → 𝐹𝑒2𝑂3. 𝐻2𝑂 + 2𝐻2O (4)
(Hydrated Ferric oxide)
Cathodic Reaction
4𝑒− + 𝑂2 + 2𝐻2𝑂 → 4𝑂𝐻− (5)
Fig. 1 to be inserted here………
Hydrated ferric oxide, i.e. rust, is formed as
a result of these reactions and it is highly
porous and has a volume 6-10 times that of
steel, causing cracking and spalling [9]. The
overall reaction mechanism is explained in
Fig. 2. At the cathode, oxygen reduction
occurs and at the anode reduction of iron
occurs through either of the reactions in
equations 6 and 7 [1]:
𝐹𝑒 → 𝐹𝑒2+ + 2𝑒− eo = -0.688 VSCE (6)
𝐹𝑒 + 𝑂𝐻− → [𝐹𝑒(𝑂𝐻)]𝑎𝑑𝑠 + 𝑒− →
𝐹𝑒(𝑂𝐻)+ + 𝐻+ + 2𝑒− eo = -0.404 VSCE (7)
Fig. 2 to be inserted here………
Formation of Fe(OH)+ depends upon
availability of OH- ions. To maintain the
electro neutrality, as Fe2+ ions are formed,
OH- ions shift from the bulk towards the
surface. At high pH, equation 7 is more
4
favourable on the surface of iron than
equation 6. Holding Fe(OH)+ ions, the
electrode potential shifts in a more anodic
direction and increases the Fe(OH)+
concentration at the steel surface. The
Fe(OH)+ oxidizes to ferric oxide, resulting
in a barrier oxide layer (Eq. 8) [1]. This is
the passive layer that protects the steel. For
corrosion to be initiated, this passive layer
must be penetrated by aggressive agents
such as chloride ions or by a reduction in
pH.
𝐹𝑒(𝑂𝐻)+ + 𝐻2𝑂 → 𝐹𝑒2𝑂3 + 4𝐻+ + 2𝑒−
eo = -0.084 VSCE (8)
2.2 Chloride Induced Corrosion
Steel remains in passive state, i.e. free from
corrosion, when it is embedded in a sound
concrete layer; but it converts to an active
state (corrosion initiates) when the concrete
around it deteriorates. Chloride ions may
penetrate from the environment or be mixed
internally and reach the reinforcement.
When chloride penetrates into concrete, the
alkalinity near the reinforcement increases
as per, Eq. 5. To maintain electro-
neutrality, Cl- and OH- ions diffuse to the
interface. Because of their greater
movement, the chloride ion concentration
will build up close to the surface, saturating
the interface with (Fe2+) and (Cl-). This will
reduce the formation of Fe(OH)+ shifting
the potential in a more cathodic direction
[1].
The chloride content required for steel
depassivation and corrosion initiation is
known as critical chloride content. If the
chloride ion concentration goes beyond this
threshold value, the passive layer gets
locally destroyed and it leads to localized
pitting corrosion [10]. The steel surface
where chloride ions attack becomes an
anode and the passivated surface becomes a
cathode [8]. The reactions involved are in
equations 9 and 10:
𝐹𝑒2+ + 2𝐶𝑙− → 𝐹𝑒𝐶𝑙2 (9)
𝐹𝑒𝐶𝑙2 + 2𝐻2𝑂 → 𝐹𝑒(𝑂𝐻)2 + 2𝐻𝐶𝑙 (10)
5
The reactions in Eqs. 9, 10 break both ferric
oxide and magnetite (Fe3O4) layers on the
steel [1].
Chlorides in concrete that are soluble in
nitric acid (sometimes referred as total
chlorides) include bound chlorides which
can be chemically bound with cement
hydration products such as the C3A or C4AF
or loosely bound chlorides with the C–S–H.
It is only the remaining chlorides, namely,
free or water-soluble chlorides which react
with steel and are responsible for its
corrosion [11].
Fig. 3 to be inserted here………
The passivity of steel depends on chloride
content. The pitting potential of steel
reduces with an increase in the chloride
content. The pitting potential (Epit) reduces
from 500 mV to -500 mV in a chloride free
structure if it becomes chloride
contaminated (Fig. 3). For a typical
corrosion potential, the critical total
chloride content varies between 0.4 - 1 %
by weight of the cement [12]. According to
BS 1504-9:2008, the chloride content limit
for reinforced concrete and prestressed
structures is 0.4% and 0.1% respectively
[13, 14]. However some studies, showed
that the ratio [Cl-]/[OH-] is a better
representation of the chloride limit in
concrete and is more critical for corrosion
[15, 16]. Higher chloride binding for a
given total chloride content, will lead to a
higher chloride threshold ratio [17]. A
threshold ratio varying from 0.3 to 40.0 has
been reported [14].
In the presence of chlorides, corrosion can
even takes place when the pH is very basic
i.e. around 12 [5]. However, more recent
research showed that this threshold limit
can be as low as 0.2% or less or even more
than 1% depending upon the environmental
and exposure conditions [13]. Therefore,
there is no scientific agreement about the
corrosion threshold limit. Hence, for each
structure, corrosion risk should be
evaluated depending upon the actual site
conditions without assuming any safe
limits. From authors’ practical experience,
the risk of corrosion should also be
6
calibrated against the actual conditions of
the structures and not only based on half-
cell or chloride values.
The effect of temperature and humidity on
chloride ion transport, concrete resistivity
and rate of corrosion should be considered
when assessing corrosion risk. The
threshold level for chloride ion
contamination can vary in different parts or
components of a structure.
In practice, following approach is adopted:
• Below 0.4%, chloride ion
concentration by mass of cement
protection of reinforcement is not
required.
• 1.0% chloride ion and evidence of
reinforcement corrosion and
concrete delamination are the upper
limits above which intervention is
required as soon as practicable.
• Between 0.4% and below 1.0%,
intervention may be deferred
providing that risk and consequence
of corrosion is evaluated as low.
• Monitoring of corrosion and defects
is necessary.
For chloride ion concentration above 0.4%,
following options should be considered and
assessed based on whole life cost analysis:
• Removal and replacement of
contaminated concrete,
• Patch repair with galvanic anodes at
the perimeter of concrete repair
patches
• No treatment to chloride
contaminated concrete but monitor
for future deterioration
• Use of Impressed Current Cathodic
Protection Technique (ICCP)
• For post-tensioned or pre-stressed
structures, the presence of lower
chloride values as low as 0.2% can
lead to stress corrosion cracking,
especially if there are voids in the
duct systems of the tendons.
2.3 Carbonation
The porosity of concrete ranges from the
micrometre to the nanometre level [18]. In
7
concrete’s pores, apart from liquid water,
adsorbed water and structural water are
present, which affects different structural
and mechanical concrete properties. This
porous structure and the natural reactivity
of concrete make it prone to a natural
degradation, called as carbonation [18].
Penetration of CO2 into the concrete layer
and subsequent neutralization of alkalis in
the pore fluid is called carbonation. It
reduces the pH of concrete to around 9
where the passive layer is not stable and
corrosion may occur [19]. CO2 attacks not
only Ca(OH)2 but also C-S-H gel and the
unhydrated cement components C3S and
C2S. Corrosion induced by carbonation can
take place over the whole surface of steel
bars due to the complete dissolution of the
passive layer around the steel [9].
The mechanism in equations 11 and 12
controls the carbonation process:
𝐶𝑂2 + 𝐻2𝑂 → 𝐻2𝐶𝑂3 (11)
(Carbonic Acid)
𝐻2𝐶𝑂3 + 𝐶𝑎(𝑂𝐻)2 → 𝐶𝑎𝐶𝑂3 + 2𝐻2𝑂 (12)
(Calcium Carbonate)
Carbonic acid formation neutralizes the
calcium hydroxide in pore water, dropping
the pH to 8 [18]. At this pH, destruction of
the passive layer is initiated and rebar
corrosion takes place with rust formation as
shown in Table 1 [9, 11, 20]. The
maximum rate of carbonation is observed at
50-70% RH [4, 17].
Table 1 to be inserted here………
2.4 Stress Corrosion Cracking (SCC)
SCC is defined as the process in which a
crack grows on a metal due to simultaneous
action of both tensile stresses and a
corrosive environment, leading to failure
without warning [1, 4, 10]. Certain
conditions lead to crack propagation due to
the anodic part of the corrosion process, this
is called anodic stress corrosion cracking
[10]. The conditions required for this type
of SCC can only rarely be reached in
concrete structures.
Another form of SCC is caused by
absorption in the metal of hydrogen gas
produced by a cathodic reaction and is
8
called hydrogen induced stress corrosion
cracking [10]. This causes loss of ductility
and crack propagation and leads to a brittle-
like fracture surface and is termed hydrogen
embrittlement [4]. This form of cracking
can be generally observed in high strength
steel used for prestressed / post-tensioned
concrete elements [10]. Other materials that
may cause this type of corrosion are
hydrogen sulphide and a high
concentrations of ammonia and nitrate
salts. When the metal potential becomes
more negative than the equilibrium
potential (Eeq,H), hydrogen evolution
occurs, which decreases linearly with pH
according to Nernst’s law [10] (Fig. 4).
Fig. 4 to be inserted here………
2.5 Stray Current Induced Corrosion
In concrete, electrolytic corrosion occurs
when a current from an external source
enters and leaves the reinforcing steel. This
is referred to as stray-current corrosion. The
currents can be generated from nearby
cathodic protection systems, railways, high
voltage power supplies etc. and travel
through electrical paths other than their
intended path [21, 22]. The currents deviate
from their intended path if they find a lower
resistance or an alternative route to flow
such as metallic pipe buried in soil [10, 21].
The current may be AC or DC depending
upon the source [10]. However, AC is
exceptionally unlikely to cause corrosion.
A cathodic reaction occurs where current
enters the structure and an anodic reaction
occurs where it leaves and returns to its
original path, leading to metal loss at the
anodic site.
In case of reinforced concrete, stray-current
interference can result in localized
corrosion where current leaves the steel and
in hydrogen embrittlement of prestressing
steel where current enters the steel if the
potential is negative enough to generate
hydrogen gas [21].
2.6 Thermodynamics of corrosion
Corrosion is a complicated process that
relies on the surrounding environment and
material, and is governed by underlying
thermodynamic and kinetic factors [23].
9
The thermodynamics of a corrosion process
decides the theoretical tendency of metals
to corrode. Thus this concept helps in
deciding conditions under which corrosion
happens and also its prevention strategy [1].
The rate at which corrosion will proceed is
controlled by kinetics of the
electrochemical reaction and is determined
by Faraday’s law of electrolysis [1].
In any electrochemical process, at
equilibrium, all reactants and products are
at unit state. Deviation from the unit
activity can be determined using Nernst
equation, Eq. 13 [1]:
𝐸𝑐𝑒𝑙𝑙 = 𝐸𝑜 − 2.303𝑅𝑇
𝑛𝐹𝑙𝑜𝑔
𝑎𝐶𝑉𝐶𝑎𝐷
𝑉𝐷
𝑎𝐴𝑉𝐴𝑎𝐵
𝑉𝐵 (13)
Where, ‘a’ is activity of reaction, V is the
stoichiometric number, A & B are the
reactants and C & D are the products of
electrochemical reaction, R is gas constant,
F is Faraday’s constant, T is absolute
temperature, n is number of electrons taking
part in the reaction, Ecell is the equilibrium
cell potential and Eo is called as standard
electromotive force of a corrosion system.
The corrosion potential of steel in concrete
is the sum of two electrode potentials i.e.
the reaction potential at the anode EFe (Eq.
14) and the reaction potential at the cathode
EO2 (Eq. 16).
Referring to the anodic reaction (Eq. 1),
𝐸𝐹𝑒 = 𝐸𝐹𝑒𝑜 − 2.303
𝑅𝑇
𝑛𝐹𝑙𝑜𝑔
[𝐹𝑒2+]
[𝐹𝑒] (14)
Substituting the values of EFe0 = 0.440, n=2,
2.303RT/F = 0.059 at T =25o C and [Fe] =1
𝐸𝐹𝑒 = 0.440 − 0.0295𝑙𝑜𝑔[𝐹𝑒]2+ (15)
Similarly, referring to cathodic reaction
(Eq. 5),
𝐸𝑂2 = 𝐸𝑂2𝑜 + 2.303
𝑅𝑇
𝑛𝐹𝑙𝑜𝑔
[𝑂2][𝐻2𝑂]2
[𝑂𝐻−]4 (16)
Substituting the values of EO20 = 0.401,
n=4, 2.303RT/F = 0.059 at T =25o C and
log[OH-] = pH-14
𝐸𝑂2 = 1.229 + 0.0148𝑙𝑜𝑔[𝑂2] − 0.0591𝑝𝐻
(17)
The E (emf) for any equilibrium system is
sum of two electrode potentials as shown in
equation 18:
E = EFe + EO2 (18)
Thus,
10
𝐸 = 1.229 + 0.0148𝑙𝑜𝑔[𝑂2] − 0.0591𝑝𝐻 +
0.440 − 0.0295𝑙𝑜𝑔[𝐹𝑒]2+ (19)
And
𝐸 = 1.669 + 0.0148𝑙𝑜𝑔[𝑂2] − 0.0591𝑝𝐻 −
0.0295𝑙𝑜𝑔[𝐹𝑒]2+ (20)
It can be observed from Eq. 20, that the rate
of corrosion is controlled by the pH of the
concrete electrolyte, the oxygen availability
and the Fe2+ ion concentration [11].
Fig. 5 to be inserted here………
The stability of different metals is estimated
by using potential-pH diagrams called
Pourbaix diagrams. A typical Pourbaix
diagram for iron in a chloride solution is
shown in Fig. 5 [9]. This depicts the change
in potential and pH as iron moves from
corroding areas to areas of passivity and
finally to an area immune from corrosion. It
can be observed that the steel is passive in
alkaline media. In concrete, the formation
of calcium hydroxide (Ca(OH)2) increases
alkalinity [18]. When chlorides enter
concrete, there is conflict between OH- and
Cl- to either passivate the steel or corrode it,
where Cl- dominates, as result pH drops and
steel moves to corrosion zone of Pourbaix
diagram from passive zone. Similar is the
case with carbonation. Ideally, to protect
the steel, the potential of iron should be
depressed sufficiently to reach the immune
zone by adopting a suitable protection
technique. However, that is very close to
the hydrogen evolution potential (lower
dotted line) at pH 12 which is where steel in
concrete lies. Thus, to avoid hydrogen
evolution, it is brought down to the area
below the pitting potentials [9].
2.7 Kinetics of corrosion
At equilibrium, at any given point on a
metal surface, the rate of forward and
backward reactions are equal [24]. In
concrete, at equilibrium, the reactions,
given by Eqs. 1 and 5, are equal at steel
surface. However, when cathodic and
anodic half cells are connected ionically i.e.
through concrete pore solution and
metallically i.e. through the reinforcement,
a net current flows between them and the
equilibrium potential shifts through
11
polarization [20, 24]. When the
concentrations of the reactants and products
at the rebar surface are the same as in the
bulk solution, the potential difference from
the reversible potential for a given reaction
is called the activation overvoltage [23].
For such reactions, the relationship between
the current density i, and potential E, is
given by the Butler-Volmer equation, Eq.
21 [1, 23]:
𝑖 = 𝑖
→−𝑖
← = 𝑖𝑜{exp (−𝛼𝑐𝐹𝜂
𝑅𝑇) − exp (
𝛼𝑎𝐹𝜂
𝑅𝑇)}
(21)
Where η = E-eeq, eeq is a reversible half-cell
potential, R is the gas constant and T is
absolute temperature.
At a large anodic over potential (η) the
cathodic term becomes negligible and
equation 21 is simplified to:
𝑖 = −𝑖a =𝑖
← (22)
𝑖 = 𝑖𝑜 exp (−𝛼𝑎𝐹𝜂
𝑅𝑇) (23)
Anodic sites on steel surface mainly
polarize through activation polarization
[20, 24]. Rearranging equation 23 gives,
η𝑎 = 𝐸𝑎 − 𝐸𝐹𝑒 = 𝛽𝑎log𝑖𝑎
𝑖𝑜 (24)
Where, Ea (V) is the polarized anodic
potential, EFe is as given in Eq. 15, βa
(V/dec) is the anode Tafel slope given by βa
= (2.3RT/αnF), io (A/m2) is anodic
exchange current density and ia (A/m2) is
the anodic current density.
Cathodic sites on the steel surface can also
polarize through both activation and
concentration polarization [24], given by:
η𝑐 = 𝐸𝑐 − 𝐸𝑂2 = 𝛽𝑐log𝑖𝑐
𝑖𝑜 −2.303𝑅𝑇
𝑛𝐹log (
𝑖𝐿
𝑖𝐿−𝑖𝑐)
(25)
Where, Ec (V) is polarized cathodic
potential, EO2 is as given in Eq. 17, βc
(V/dec) is the cathode Tafel slope given by
βa = (2.3RT/αnF), io (A/m2) is cathodic
exchange current density, ic (A/m2) is
cathodic current density and iL is limiting
current density given by:
𝑖𝐿 =𝐷𝑛𝐹𝐶𝑂2
𝑑 (26)
Where d (m) is diffusion layer thickness, D
(m2/s) is the oxygen diffusion coefficient,
CO2 (mol/m3 of pore solution) is the
concentration of dissolved oxygen on the
12
concrete surface [24]. Concentration
polarization only occurs when oxygen
availability at cathodic sites is not enough
to sustain the oxygen reduction process
[20].
The corrosion process kinetics can be
graphically represented on a potential vs
current plot called as Evan’s diagram (Fig.
6).
Fig. 6 to be inserted here………
As shown on the plot, the point where the
cathodic and anodic curves meet gives the
value of corrosion potential (Ecorr) at which
the external current is maximized [1]. The
current at this potential is called the
corrosion current (Icorr) which can be used
to calculate the corrosion rate of any metal.
The protection current (ipro) required in the
external circuit to stop corrosion can also be
estimated from the Evan’s diagram by
extending the cathodic polarization line
until it reaches the anodic equilibrium
potential [1]. This forms the basis of
cathodic protection.
3 Corrosion Mitigation Techniques
Due to the increasing demand for longer
service lives for infrastructure and the high
cost involved in building and maintaining
it, the repair of concrete structures has
become extremely important [25]. The
repair and protection techniques for
concrete are based on chemical,
electrochemical or physical principles [13].
Since corrosion is an electrochemical
process, its main components are the
cathode, the anode and the electrolyte (in
form of concrete pore water). The absence
of any of these three components can
restrict the corrosion process.
Repairs to corrosion damaged concrete
structures are broadly categorised into two
classes: conventional repair methods and
electrochemical methods:
Conventional repair methods involve the
removal of delaminated/spalled concrete
and replacement with new alkaline concrete
and also patching, coatings, sealers,
membranes and barriers, encasement and
overlays, impregnation and the use of
13
corrosion inhibitors [26]. These are
generally temporary techniques for
corrosion prevention and can lead to
acceleration of corrosion in nearby repaired
areas [27]. After serious damage has
occurred, they are generally costly and less
effective than electrochemical methods [28,
29].
Electrochemical techniques include
cathodic protection, cathodic prevention,
electrochemical realkalisation and
electrochemical chloride removal and are
effective methods for corrosion prevention
and mitigation [10, 30, 31]. In
electrochemical techniques, the chemical
reactions and current flows due to corrosion
are suppressed by the application of an
external DC supply with the help of an
anode (temporary or permanent). Direct
current is passed from the artificial anode to
the reinforcing steel to be protected. The
current passes as a flow of ions through the
pore water of the concrete to the
reinforcement [32]. The advantage of such
techniques is that only broken concrete
needs to be removed and repaired [10].
The following sections describe different
corrosion protection methods as suggested
by BS 1504-9 [13]:
3.1 Corrosion Inhibitors (CI)
Corrosion inhibitors are chemical
substances that reduce corrosion rates
without significantly changing the
concentration of any other corrosion agents
[1, 33]. These inhibitors are chromates,
nitrites, benzoates, phosphates, stannous
salts and ferrous salts [1]. They are
relatively of low cost and easy to handle as
compared to other preventive measures for
corrosion protection. Depending on the
basis of their action, they can be anodic,
cathodic or mixed inhibitors.
Fig. 7 to be inserted here………
Anodic inhibitors, for example calcium
nitrite, supress the anodic corrosion
reaction, hence reducing the corrosion rate
by increasing the corrosion potential of
steel, (Fig. 7a). This is the most widely used
14
inhibitor for concrete [34]. Cathodic
inhibitors, for example sodium hydroxide,
supress the cathodic corrosion reaction,
hence acting on the oxygen reaction and
reducing the corrosion rate by decreasing
the corrosion potential of steel, (Fig. 7b).
The other type is mixed inhibitors which
supress both anodic and cathodic reactions
and reduce corrosion rates without
changing the corrosion potential by surface
adsorption over steel bars and thus forming
a protective layer (Fig. 7c) [35]. However,
anodic inhibitors have more pronounced
effect [36]. Lee et al., 2018 [37]reviewed
various types of inhibitors and suggested
that more extensive investigation is
required to study the effectiveness of
mixed/organic inhibitors in long term
applications under various scenarios such
as chloride content, types of cement etc.
Integral corrosion inhibitors are substances
which, while not preventing ingress of
chlorides into concrete, inhibit corrosion of
steel. Only those inhibitors that can prolong
the service life due to chemical or
electrochemical interactions with the
reinforcement can be considered as CI for
concrete [10]. Neville (1995) states that
nitrites of sodium and calcium have been
found to be effective in corrosion protection
[8]. The action of the nitrite is to convert
ferrous ions at the anode into a stable
passive layer of Fe2O3. The nitrite ion
reacts specifically with the chloride ion.
However, it is has not been demonstrated
that corrosion inhibitors are permanently
effective, they may simply delay corrosion.
If desirable, the accelerating effect of
nitrites can be controlled by the use of a
retarding admixture. A potential problem
with sodium nitrite is that it increases the
hydroxyl ion concentration in the pore
water, and this may increase the risk of
alkali-aggregate reaction.
Other type of inhibitors are migratory
inhibitors, which are applied as liquid to the
concrete surface and form a self-
replenishing monomolecular protective
layer on steel [34, 38]. They reach the steel
surface by migrating through concrete by
15
capillary infiltration and vapour diffusion
and gets deposited on it by polar attraction
[38]. Malik et al. (2004) studied the
performance of migratory corrosion
inhibitors (MCI) which are proprietary
blend of surfactants and amine salts in a
water carrier and can either be applied on
concrete surface or can be used as corrosion
inhibitors on rebar. [39]. Bavarian et al.
(2003) stated that MCI based on amino-
carboxylate chemistry are the most
effective at interacting at the anode and
cathode simultaneously [40]. Soylev and
Richardson (2008) [33] presented a review
on the most commonly used corrosion
inhibitors in concrete viz. aminoalcohols
(AMA), calcium nitrites, and sodium mono
fluorophosphates (MFP). The research
showed great concern on the long term
effectiveness of CI in real environments
and proposed a detailed analysis to study
the factors influencing migrating CI’s
protection efficiency. From practical
experience, the major problem with
migrating CI is the depth of penetration. It
may not be deep enough to reach the steel.
This depends on quality of concrete and the
porosity. The depth of penetration can also
vary in different parts of the structure
resulting in non-uniform protection.
Corrosion inhibitors are water soluble and
may leach out from concrete [36].
Moreover, the commonly used inhibitors
are costly and toxic in nature [41]. Thus,
there is great need for replacing harmful
inhibitors with cost-effective,
environmentally friendly, non-hazardous
alternatives. Abdulrehman et al. 2011 [33]
reviewed various possible CI effective in
concrete and their mechanism. Their review
concluded that Amines, alkano amines,
amino acids, mono, poly carboxylates,
amino–alcohol based inhibitors, BTAH,
organic heterocycles and green products
could be successfully used as an effective
inhibitors for concrete protection. Green
Inhibitors as the future of CI in concrete
should be explored in more detail. Some of
the options available as green inhibitors
were reviewed. Agro-waste/natural
16
products and medical waste such as heena,
neem, bamboo, penicillins, cefatrexyl etc.
are non-toxic and have negligible harmful
environmental impacts, and thus may
replace traditional toxic corrosion
inhibitors [42–44]. However, this is still a
new concept and needs to be researched.
Huang and Wang, 2016 [26] studied the
combined effect of ECR and CI (Calcium
Nitrite) in chloride removal. They
concluded that penetration of CI increases
in presence of electric field which
accelerates passivation of rebar. Similar
results were reported by Lee et al., 2018
[37] suggesting enhanced effectiveness of
CI when electrochemically injected to
improve protect steel in both carbonated
and chloride contaminated concrete.
However, the concept is of great interest but
requires more study.
3.2 Using Alternative reinforcement
To prevent corrosion of reinforcement in
concrete, an alternative is to use
reinforcement made of corrosion resistant
material such as stainless steel or Fibre
Reinforced Plastic (FRP).
3.2.1 Stainless Steel (SS) Rebars
Pitting is the only form of corrosion that can
occur in SS in concrete. Other forms of
corrosion such as intergranular corrosion,
stress corrosion or crevice corrosion
requires an extremely aggressive
environment which is very unlikely to
occur [10]. The corrosion resistance of SS
bars is significantly higher than carbon or
mild steel because of the higher stability of
their passive film [10]. The film is rich in
chromium, and has a good bond with the
parent metal and is self-healing in an
oxygen rich environment [45].
In an alkaline solution, Moser et al. (2012)
reported that all high-strength stainless
steels HSSSs (Austenitic, Martensitic and
Duplex) show high corrosion resistance at
Cl- concentrations from 0 to 0.25M. But as
the Cl- concentration increases to 0.5M and
for a carbonated solution, only S32205 and
S32304 i.e. duplex grades exhibit low and
moderate corrosion susceptibility
17
respectively. S32205 even shows high
corrosion resistance at 1.0M Cl-.
Enhancement of nickel (Ni) and nitrogen
(N) in the austenite phase enhances its
corrosion resistance when compared with
the ferrite phase [46].
Duplex steel 1.4362 (AISI S2304) and
austenitic steel 1.4401 (AISI 316) have very
good corrosion performance when exposed
to a chlorine environment [47]. This is due
to good protective properties of the passive
film, enriched with Cr, Ni and Mo. Also,
steel types with low Ni content, but with
high N and Molybdenum content perform
well in a chloride rich environment. The
Concrete Society technical Report 51
recommends austenitic and duplex steel for
use as reinforcement in concrete [45].
However, it is too expensive to use SS as a
replacement for mild steel reinforcement in
most applications (the cost is almost 6 to 9
times higher) [45]. Though, its use can be
prioritised with an outer layer of stainless
steel but leaving the rest as carbon steel.
But, when they are coupled with carbon
steel, there is risk of galvanic corrosion of
carbon steel [10, 45]. However, the
corrosion rate is low when carbon steel is
coupled with stainless steel compared to
when corroding carbon steel is coupled
with passive carbon steel [45, 48]. For the
application of CP to structures having
Austenitic and Duplex SS bars, the
minimum negative potential recommended
for protection is 0.6V [49]. The risk of
hydrogen embrittlement should be assessed
on a case by case basis by determining the
safe potential of the specific type of SS used
in the structure.
3.2.2 Fibre Reinforced Plastic (FRP)
Rebars
Fibre Reinforced Plastics (FRP) are
composite materials consisting of a matrix
phase and a fibre phase. They have high
corrosion resistance, light weight and high
tensile strength [50]. Generally, they are of
4 types: aramid fibre (AFRP), glass fibre
(GFRP), carbon fibre (CFRP) and basalt
fibre (BFRP). Aramid fibres are sensitive to
environmental degradation and glass fibres
18
degrade with time when exposed to alkaline
or acidic environments. Carbon and basalt
fibre are highly resistant to both alkaline
and acidic environments.
Waldron et al. (2001) studied the effect of
chloride on durability of FRP [51]. They
observed that CFRP bars exposed to
combined chloride/moisture attack in
concrete show very little degradation with
time, with aggressive exposure or
temperature. However, AFRP and GFRP
bars showed up to 50% loss of strength. Suh
et al. (2007) evaluated the effectiveness of
FRP wrapping in slowing down corrosion
in heavily contaminated concrete
incorporating carbon and glass fibre in a
marine environment, by monitoring the
corrosion rate and also studying the role of
fibre layers. They observed no difference in
potential readings in any of the CFRP and
GFRP wrapped specimens. Additionally,
the number of FRP layers had a relatively
minor effect on the potential reading [52].
Thus, the difference between corrosion
rates in the CFRP and GFRP wrapped
specimens is very minor. However, ACI
440.2R-08 (2008) [53] recommends not to
use FRP reinforcement without arresting
the ongoing corrosion and repairing any
degradation to the substrate, if steel in
concrete is corroding or the concrete
substrate is degrading, as FRP is not going
to stop ongoing corrosion to the existing
reinforcement.
Hence, it is clear that CFRP provides more
corrosion resistance than GFRP or AFRP
bars for concrete exposed to marine
environments. However, CFRP bars have a
very high cost. As an alternative, BFRP
bars shows good corrosion resistance and
are cheaper as compared to CFRP [54].
BFRP bars could be an economical solution
compared to other FRP bars and SS bars.
Moreover, basalt fiber has much higher
thermal stability as compared to other
fibers, having a melting point near 1400oC.
Thus, it can also provide resistance against
fire. However, there has been limited study
of it. In practice, a coupled application of
CFRP and cathodic protection is
19
recommended. More research is needed
into these areas.
3.3 Steel Coating
Coatings act as a physical barrier to
corrosion. Coatings should have high
adhesion and their protection depends on
their porosity and permeability [4].
Coatings suitable for rebar protection in
concrete can be metallic, organic or
cementitious. These coatings are non-
reactive in a corrosive environment and
protect steel from mechanical damages.
Metallic coatings for steel reinforcement
are of two types: Sacrificial and noble
coating. Sacrificial coatings are made up of
less noble metals such as zinc and cadmium
and provide protection to steel by
sacrificing themselves compared to the
underlying cathode i.e. parent metal [55].
Unlike, non-sacrificial coatings, even if
they break during fabrication,
transportation or during service, the parent
metal remains protected [55]. They can be
applied by dipping, electroplating,
spraying, cementation, and diffusion [56].
The most commonly used metallic coating
is using zinc metal and is called
galvanizing. Galvanized reinforcement can
withstand higher exposure to chloride
environments, compared to carbon steel
and can even provide protection against
carbonation in concrete [57]. However, the
useful life of zinc coating depends upon
coating thickness. A large amount of zinc
can be lost before the parent metal is
attacked owing to its sacrificial properties.
It is mostly suitable for concrete exposed to
carbonation [36]. However, the main
problem with galvanizing is the formation
of hydrogen gas leading to a loss of bond
between the coating and the cement paste
[58]. One way to protect this is by
increasing the passivation time of zinc by
adding soluble inhibitors such as
chromates. However, due to its toxic and
carcinogenic nature, EU limits its use.
Bellezze et al. 2018 [58] studied various
soluble inhibitors to reduce hydrogen
evolution of galvanized steel when
embedded in concrete and discovered
20
nitrites suitable to decrease H2 evolution by
shifting the potential to a more positive
value. However, a non-toxic solution for
this remains to be discovered. Moreover,
the risk of stress corrosion cracking in
galvanised bars under high stress is high.
Non- sacrificial coatings include Ag, Ti, Ni,
and Cr which provide barrier protection to
steel i.e. protect the steel by forming a
passive layer on it. In this, the parent metal
acts as an anode compared to the cathodic
passive film. It may lead to localized
attack, if broken during fabrication or
transport.
Organic coatings include epoxy coating,
polyvinyl chloride, poly-propylene,
phenolic nitrite, polyurethane etc. and
isolate steel from aggressive agents, oxygen
and moisture. Most widely used, bonded
epoxy bars have electrostatically applied
epoxy powder on thoroughly cleaned and
heated bar [4]. They provide excellent
corrosion protection without a significant
increase in material cost and are not
consumed during their operational life.
However, the major difficulty is protecting
them from abrasion and mechanical
damage during transportation and handling
and thus becoming ineffective in corrosion
protection [55, 59, 60]. Hence, frequent
patch-ups are required. Moreover, the bars
are not electrically continuous due to the
epoxy and thus CP systems are not cost-
effective. There is also a risk of significant
pitting because the small defects in coating
give a small surface area of an anode and a
high corrosion current density. Ali et al.
(2015) reported that that epoxy bars are not
efficient for long term corrosion protection
due to their porous and hydrophilic nature
[61, 62]. In practice, the durability of epoxy
coated reinforcement is of great concern
due to its failure record in high chloride
environments and localized corrosion
conditions.
3.4 Concrete Coating
The application of surface coatings and
treatment on a reinforced concrete surface
provides a cost-effective and relatively
simple approach for protection. The main
21
objective of surface treatment is to provide
a barrier between concrete surface and
environment, thus make it less permeable to
ingress of aggressive substances and
moisture and also increasing the concrete
resistivity [10]. Hence, sometimes they are
also referred as sealers. They are most
beneficial if corrosion is due to carbonation.
Chloride induced corrosion attracts a lot of
moisture, and surface treatment may not be
able to stop it [10]. They can be divided into
3 classes: organic coatings, hydrophobic
impregnation, and cementitious coatings
[10].
Organic coatings form a continuous
polymeric film on the concrete surface, thus
blocking penetration of carbon dioxide and
chloride ions. Coating thickness ranges
from 100-300 µm [10]. Organic coatings
can be dense or vapour permeable coatings.
Dense coatings are based on epoxy,
polyurethane or chlorinated rubber polymer
and do not allow the moisture inside
concrete at time of application to evaporate,
which may lead to a loss of adhesion and
hence coating failure [10]. Vapour
permeable coatings are generally acrylates
and allow the concrete to dry out, reducing
risk of degradation or blistering from
trapped moisture. In case of carbonation,
they will not remove already present
contamination, but prevent further ingress
of carbon dioxide. In case of heavily
contaminated concrete, the coating may fail
due to the formation of salt crystals [63].
Coating breathability is important, all anti-
carbonation and chloride coatings must be
breathable. Non-breathable coating can
only be used if only part of the surface area
is coated allowing for moisture to escape
from the exposed faces.
Hydrophobic Impregnation materials
include silanes, siloxanes and silicate-based
compounds. They penetrate into the
concrete surface and form a water repellent
lining on the pore walls, hence preventing
the penetration of chloride ions and other
aggressive agents. Since pores are left open,
this is also vapour permeable in nature [10].
They are not effective against standing
22
water and are most suitable on vertical
surfaces where the water can run off [63].
Although, silane and siloxane polymers
have shown promise as corrosion protection
treatments, there has been limited study on
use of silanes as an additive to polymer
concrete. Liu et al., 2018 [64]studied the
effect of silanes as an additive in concrete
and observed silanes showing excellent
resistance to corrosion, freeze thaw and
carbonation
Cementitious Coatings can be true cement
based coatings (<10 mm thick) applied by
brushing or in form of overlays (few
centimetres thick) applied by plastering or
spraying, such as shotcrete [10]. Polymer
modified cementitious coatings are easier to
apply than coatings requiring a dry
substrate and overcome most of the
problems with coating concrete [63]. They
have good carbonation and chloride
penetration resistance [10]. A few
millimetres of these coating is equivalent to
almost 100 mm of normal cover, but the
major issue is its long term bond.
Cementitious coatings have been used in
combination with an epoxy coated glass
scrim to provide restraint to concrete that
has a risk of delamination [63].
Surface treatment is affected by many
parameters such as air permeability, bond
strength, substrate properties and
application methods [65]. Goyal et al. 2018
[66] studied the bond behaviour of zinc rich
paint coating and observed that substrate
roughness affects the bond behaviour of
concrete the most. The higher the exposure
of aggregate on the concrete surface, the
lesser the bond strength. In practice, grit
blasting has proven to be the best method of
preparation to achieve highest bond. Rotary
water jets have also been used successfully.
The application of a coating will affect
future inspection and testing of structures.
For example, half-cell mapping cannot be
done easily and impregnating a coating also
affect the reading of half-cell mapping. Pan
et al. 2018 [65] reviewed various concrete
coatings and suggested some future
research such as: the use of polymer/clay
23
nanocomposite as organic coatings and the
effect of cement type on the selection of
surface treatment for various coatings.
3.5 Cathodic Protection (CP) or
Cathodic Prevention (CPre)
These are electrochemical techniques used
for preventing corrosion initiation in
reinforced concrete structures subjected to
chloride penetration [30, 67, 68]. U.S.
Federal Highway Administration
memorandum in 1982, stated that ‘CP is the
only rehabilitation technique that was able
to stop corrosion in salt-contaminated
bridge decks irrespective of level of
chloride in concrete’ [69]. CP can be
applied to control corrosion in chloride
contaminated structures or to prevent
corrosion in new structures [68]. The latter
technique is referred as cathodic prevention
[70]. CPre requires approximately one-
tenth of the energy of CP. Thus, cathodic
protection systems for new structures
present lower installation and operational
costs, use less material due to lower current
demand and are more environmentally
friendly when compared with concrete
patch repairs and retrofitted cathodic
protection during the operational life of a
structure [71]
When compared to conventional methods
of protection, cathodic protection is
cheaper, easier, can treat a larger area
simultaneously and most importantly does
not give rise to incipient anode problems.
Therefore, it is most suitable repair
technique to be employed in chloride
contaminated structures [31].
3.5.1 Types of CP
Cathodic protection is applied in two ways:
Sacrificial Anode Cathodic Protection
(Passive system) and Impressed Current
Cathodic Protection (driven by an external
power supply), and more recently a new
system with the properties of both methods
has been introduced and is called a hybrid
system.
Sacrificial Anode Cathodic Protection
(SACP)
24
Sacrificial cathodic protection is generally
used for the protection of underground
pipelines and submerged structures. In
SACP less noble metals than steel like zinc
or aluminium are connected with the steel
bar and the dissolution of this anode metal
provides current instead of an external
power supply (Fig. 8) [72, 73].
Fig. 8 to be inserted here………
DC current is generated due to the potential
difference between the steel to be protected
(cathode) and the sacrificed metal (anode)
[67, 74]. Its advantages are simplicity, cost
of monitoring and maintenance, and the
availability of wide range of anodes [74,
75]. Disadvantages with the SACP are a
requirement for the periodic replacement of
anodic metal due to its dissolution in the
process, limited control over the system and
the low driving voltage which may be
inadequate to provide full cathodic
protection in all situations [74].
Alloys made from zinc, aluminium and
magnesium which are less noble (higher
electrical potential) with respect to carbon
steel reinforcement are generally used as
sacrificial anodes [74, 76, 77]. However,
during use, Al and Mg oxides can attack
concrete [78]. SACP is more effective for
CPre than for protection. SACP is limited
to small targeted repairs with short life-
times [67, 79]. Kean and Davues (1981)
stated that SACP is less liable to cause
interactions with adjacent structures and
unconnected metal parts in the same
structures [67]. According to Byrne et al
2016, SACP is a safer option for pre-
stressed structures as there is less risk of
hydrogen embrittlement.
Common anodes used for SACP include
metallic coating anodes (zinc or
aluminium-zinc-indium thermally sprayed
onto the concrete), anode jackets, adhesive
zinc sheet and discrete repair anodes [67,
77, 80]. The application of these anodes is
limited, as they need to be replaced after
0.3-0.5 m maximum depending on the
amount of steel.
There has been a lot of research carried out
on the use of SACP for corrosion
25
mitigation, but there is still concern about
the use of SACP for corrosion control in
already contaminated concrete., Galvanic
anodes are extensively used along with
patch repair to prevent the incipient anode
affect, however their service life is not long
enough (currently 10-15 years). In order to
protect them, coating patch repaired
concrete with embeddable galvanic anodes
should be considered. Experience suggests
that galvanic anodes should not be used in
tidal zone unless protected with jackets.
Impressed Current Cathodic Protection
(ICCP)
In this method, a small direct current (DC)
is supplied from a permanent anode (which
can be fixed at the surface or into the
concrete) through the concrete electrolyte
to the steel bars. It uses a permanent,
external power source; such as a rectifier
powered from the main supply, solar cells,
batteries, fuel cells or other means to
deliver protective current to the steel
reinforcement [77]. The current passed
should be sufficient enough to halt the
anodic reactions and cathodic reactions can
occur at steel surface to produce hydroxyl
ions. The production of hydroxyl ions will
increase the alkalinity and repassivation of
the steel bar and strengthening of passive
layer will take place [70]. The potential of
steel is brought to a value more negative
than the corrosion potential and thus steel
bars become a cathode. A schematic
diagram of ICCP systems is shown in Fig.
9.
Fig. 9 to be inserted here………
The ICCP system is much more commonly
used in reinforced concrete than SACP as it
can address significant corrosion issues in
large structures with longer life
expectancies [67]. The current density
applied varies from 1 – 2 mA/m2 for
cathodic prevention and 5 – 20 mA/m2 for
CP with respect to steel surface area.
The beneficial effects of ICCP include [32,
81]:
PRIMARY
26
• Potential of reinforcement is made
more negative
• All locally generated corrosion cells
are overcome
SECONDARY
• Aggressive chloride ion removal via
ionic migration
• Rise in the concentration of
hydroxyl ions at the steel
reinforcement
After application of CP or CPre on a
structure, it should be operated throughout
the service life of the structure [10]. The
anode system should be able to perform
according to the design parameters and
should not result in performance
degradation either of concrete-anode
interface or the anode itself during the
design life. The ICCP system is preferred in
dry areas, due to high concrete resistivity in
a dry environment. The flow of current can
be regulated depending on the resistivity
[74].
Anodes for ICCP need to be good electrical
conductors, have low corrosion rates and be
able to tolerate high currents without
forming resistive oxide layers. Common
anodes used for ICCP include activated
coated titanium wire, ribbon or mesh,
organic coating such as polymer or coke
and conductive cementitious anodes [67,
80, 82]. Table 2 gives a comparison
between SACP and ICCP systems.
Table 2 to be inserted here………
The cause of failure of ICCP is normally
early problems or end of component life.
The contractor deals with early problems as
part of defects liability period, normally 1
or 2 years. Later problems should be dealt
with when the ICCP elements reach the end
of their design lives. Early issues can
include failures of reference electrodes
(usually due to lack of contact to the
concrete due to grout shrinkage), instability
of reference electrodes due to leaching out
the solution, debonding of the overlay on
MMO/Ti mesh systems, localised high
current and consumption of the anode, loss
27
of connection at the interface of conductive
coating and concrete due to drying out of
concrete when electro-osmosis occurs and
water entering junction boxes. However,
anode failure does not cause immediate loss
of protection, steel will remain in a passive
state for few years [83].
The installation of pseudo reference
electrodes (MMO/Ti, graphite or stainless
steel) together with true reference
electrodes, gives an alternative monitoring
means with long life but are less accurate.
During the service life there could be other
problems like the client failing to pay the
electricity bill, or transferring the data SIM
card and therefore operation and
monitoring are interrupted. Thus, having a
maintenance contract in place is equally
important.
Polder (2011) conducted a survival analysis
on 105 structures and stated that mean
service life of any CP system is 15 years
without intervention. There is a 10%
probability that a CP system needs
maintenance at an age of about 7 years or
less and 50% probability that maintenance
is needed at an age of 15 years or less [83].
Hybrid Cathodic Protection
A recent advancement in CP systems is
hybrid CP. In hybrid system, a temporary
impressed current is used in combination
with a low maintenance galvanic system to
restore and maintain alkalinity [84]. The
anodes mainly used with this system are
discrete anodes connected to titanium wire
for impressing the current [67]. The same
anode is used for both impressed and
sacrificial systems [84]. Typically, the
system involves supplying a very high
current for one week and then running the
system galvanically [84]. The potential is
mainly achieved by realkaization of acidic
sites, maintaining high pH and hence
restoring steel passivity [84]. This is a new
concept and has not yet been significantly
explored. Glass et al. 2008 developed a
hybrid electrochemical treatment
consisting of a pit re-alkalisation process
and supplementary galvanic protection to
induce and maintain a high pH at the steel.
28
The treatment was able to reduce extreme
corrosion and requires low maintenance
[85].
Vector Corrosion Technologies, United
Kingdom recently developed a fusion
hybrid anode with a battery inside a casing.
The anode initially operates in ICCP mode
and after an impressed current phase,
switches over to galvanic mode
automatically without external human
intervention. The anode is claimed to be
effective for a service life of approximately
30 years. Hybrid cathodic protection has the
potential to be the future of CP systems, but
requires further development in terms of
type of anode, installation and operation.
Table 3 summarizes some of the existing
anode types and their performance
characteristics suitable for different types of
CP system.
Table 3 to be inserted here………
3.6 Electrochemical Realkalisation
The purpose of this technique is to provide
long term corrosion protection to steel in
carbonated concrete [86]. However, the
carbonation must be confirmed as the cause
of the corrosion before it is applied. In this
case, for a short period, a small electric field
is applied between steel in concrete and an
alkaline electrolyte solution containing
carbonate or hydroxyl ions and a temporary
external anode (Fig. 10) [87–89]. It requires
a charge 50 to 500 times greater than CP i.e.
up to 0.5-1 A/m2 of steel area and thus the
initial cost is higher than CP. Typical
treatment time is 6-8 days [86].
Fig. 10 to be inserted here………
During the realkalisation process, oxygen is
reduced at steel and even hydrogen can be
generated if very negative potentials are
reached [10]. These reactions create
hydroxyl ions on the steel surface and help
the steel to achieve its passivity. The
alkalinity of carbonated concrete is raised
and the pH is maintained above 10.5 to
restore and maintain a passive protective
layer around the reinforcing steel and hence
it is called electrochemical realkalisation
[28, 90, 91]. Electrolyte solutions of
29
sodium, potassium and lithium may be used
[88]
Platinised titanium mesh and steel mesh
anodes in the alkaline electrolyte are
conventionally used for the realkalisation
process in structures [90]. Sodium
carbonate solution is generally used as an
electrolyte [9, 32]. High current densities
and voltages can cause some side effects,
such as the possibility of hydrogen
embrittlement in case of high strength
prestressing steel when the potential
becomes more negative than -1000 mV vs
SCE and the risk of alkali-aggregate
reaction, bond degradation and anodic
acidification [9, 10, 32, 86, 89].
3.7 Electrochemical Chloride
Extraction (ECE)
This technique is suitable for treating
heavily chloride contaminated and
corroded structures. It is a non-destructive,
temporary and cost effective rehabilitation
technique [29]. The application of an
electric field for a short period of time
between the steel bar and the externally
deposited anode surrounded by alkaline
electrolyte solution removes the negatively
charged chloride ions present at the steel
surface (Fig. 11) [92]. These ions migrate
towards the external anode layer and
thereby reduce the chances for corrosion
initiation [91, 93]. Moreover, hydroxyl ions
are also produced by the reduction of
oxygen and water due to reaction at steel
surface, providing alkalinity to concrete in
vicinity of the rebar [92]. It requires charge
50 to 500 times higher than CP i.e. up to 1-
2 A/m2 of steel area and thus the initial cost
is higher than CP. A typical treatment time
is 6-8 weeks [20, 26, 32, 59].
Fig. 11 to be inserted here………
Catalyzed titanium mesh and steel mesh are
most commonly used as anodes in the
chloride removal process [10]. The most
commonly used electrolytes are water,
calcium hydroxide solution and lithium
borate solution. It is not recommended to
use this technique with prestressing wires
due to the risk of hydrogen embrittlement
and it may also create a risk of alkali silica
30
reaction due to increased hydroxyl ion
concentrations near the steel surface during
the protection process [10, 26, 86, 89].
Table 4 summarizes advantages and
limitations of different corrosion protection
techniques.
Table 4 to be inserted here………
4 Conclusion
From the review, it is evident that corrosion
of reinforcement in concrete is a major
issue and needs to be considered when
designing concrete structures exposed to
aggressive environments. Understanding
the corrosion process and its
thermodynamic and kinetic nature is
important for designing a suitable
protection strategy. There are various
protection techniques available such as
corrosion inhibitors, alternative
reinforcement, steel and concrete coating
and electrochemical techniques. However,
electrochemical techniques are generally
more effective than conventional methods.
The suitability of any mitigation technique
varies from structure to structure depending
upon value engineered, practicality and
economic considerations. There is no single
best solution for every structure and each
one needs to be evaluated on case to case
basis. In practice, sometimes, cost pressure
based upon client’s requirements leads to
the adoption of a particular solution.
31
Table 1 Corrosion state at different pH levels [11]
pH State of reinforcement corrosion
<9.5 Corrosion initiation
8.0 Passive layer disappears
<7.0 Catastrophic corrosion occurs
Table 2 Comparison of galvanic and impressed current cathodic protection system
Table 3 Different anodes and their properties used for CP system
Technique Advantages Disadvantages References
SACP
• Simpler
installation, design
and low
maintenance
• No external power
source required
• Less liable to cause
interaction
• No control system
• Low risk of
hydrogen
embrittlement
• Can be applied to
prestressed
structures
• Less experience in reinforced
concrete
• Unable to control current
• Unknown degree of protection
• Additional anode required if current
demand changes
• Limited service life
• Not adequate in high resistance
environment
• Low driving voltage, thus can be
used only in less resistive concrete
• Monitoring need to be considered at
the design stage.
• Anodes can be large and intrusive
compared to ICCP
• Non-uniform anode consumption
[9, 32, 67, 74,
77, 94]
ICCP
• Commonly used in
reinforced concrete
• Controllable
current
• Adequate in high
resistance
environment
• Higher life span
• Minimal effects on
concrete
• Monitoring shows
it is effective
• Need permanent external power
source and continuous monitoring
• Greater risk of interaction
• External power source and
monitoring system vulnerable to
damage and atmospheric corrosion
• Service life of control equipment,
cabling and silver/chloride
electrodes will be around 20
years. Control equipment may
also need maintenance in
between. Cable routing could be
difficult and require expensive
access
• Greater risk of hydrogen
embrittlement
• Specialist expertise required
• Vandalism of the equipment is
also a major factor to be
considered especially in remote
and secluded areas.
[9, 32, 67, 74,
77, 94]
32
Anode Type
Expected
Service
Life
(years)
Required
Current
Density
(mA/m2)
Estimated
installation
cost of
anode
(£/m2)
Suitable
Environment Other Performance Characteristics
Conductive
Organic
Coatings
(ICCP)
5-15 2-20 100-300
• Not suitable
for wet or
structures
• Not suitable
for running
surface
• A series of conductors fixed to
concrete surface or integrated into
the coating.
• Optimum dry film thickness of
coating is 0.25-0.5mm
• Shortest life of anode systems and
are rarely applied in the UK any
more. However, some of the
earliest conductive coating
anodes are more than 20 years old
i.e. exceeding their design lives.
Metallic
Coatings
(ICCP/
SACP)
10-25 2-20 200-400
• May be
suitable for
wet
structures
• Not suitable
for running
surface
• Zinc for SACP and ICCP; Al-Zn-
In for SACP; Ti for ICCP
• Primary anodes feed connections
from Ti, stainless steel or brass
plates fixed to concrete surface
• Thermally sprayed Zinc applied
by arc or flame spraying having
optimum thickness of 0.1-0.4 mm
• One anode per 10m2 is typical
Discrete
Anodes
(SACP,
Hybrid)
25-50 ---- 160-400
• Suitable for
wet
structures
• Suitable for
running
surface
• Prevents the repaired area from
causing new anodic corrosion
nearby.
• Similar discrete anodes can be
installed in holes cored or cut into
the concrete and wired together
Conductive
Cement
Overlay
(ICCP)
25 2-20 150-350
• Suitable for
wet (not
tidal)
structures
• Suitable for
running
surface
• Contains granular carbon or
carbon fibres with metallic
coating as the conductive
medium.
Adhesive
Zinc Sheet
(SACP)
25-50 --- ----
• May be
suitable for
wet
structures
• Not suitable
for running
surface
• Rolls of Zn foil, typically 0.25mm
thick coated on one side with
ionic conductive adhesive gel
(hydrogel)
Anode
Jackets
(ICCP/SA
CP)
120 110 200-400
• Suitable for
wet
structures
• Suitable for
running
surface
• Expanded anode mesh in
permanent glass-reinforced form,
grouted to concrete piers, piles or
columns
• Ti mesh for ICCP, Zn mesh for
SACP
• High initial cost
Activated
Titanium
(ICCP)
25-100 110 200-400
• Suitable for
wet
structures
• Suitable for
running
surface
• Mesh, strip, wire or tube activated
Ti anodes, coated with mixed
metal oxides with an overlay or
cast into slots or drilled holes or
fixed to surface under GRP
casings
• High initial cost
33
Table 4 Comparison of different corrosion prevention techniques
Repair
Technique Applications Advantages Service Life
Estimated
cost (£/m2) Limitations
Referen
ce(s)
Corrosion Inhibitors
• Mixed
with fresh
concrete for new
structures
• Penetrated
into
hardened concrete
for repair
• Used as a
surface
treatment
on bars
• Easy to handle
• Compatible
with CP
• Low Cost
• Limits amount
of concrete
needed to be removed
• Delay initiation
of corrosion in
concrete
exposed to chloride attack
and
carbonation.
10-15 years or less
20-50
• Shorter long-term
performance
• Toxic in nature
• Less significant effect
after corrosion initiation
• Issues in uniform and
effective spread along reinforcement
• Unknown level of
protection
[35, 59, 62]
Alternative
Reinforcement
• Alternative
to carbon
or mild
steel
• Higher
corrosion
resistance than conventional
steel
• FRP bars
highly resistant
to both alkaline and acidic
environment
• Less prone to
damage during
handling compared to
coated
reinforcement
• Can be used
with electrochemical
techniques
• Long term
solution
• Needs
consideration
to not use in the
whole structure
because of cost
SS-Almost
10 times than
mild steel bar
• Expensive
• Risk of galvanic
corrosion in carbon
steel when coupled
with SS
[10, 47,
51, 59]
Steel Coating
• Applied on
steel reinforcem
ent and
acts as a
protective
barrier
• Available in
numerous
formulations
• Highly
corrosion
resistant
• Protects steel
from
mechanical
damage
• Protects steel
from chloride
attack and
carbonation
• Cost-effective
Max 15 Years 20-50
• Damage during
fabrication or handling may lead to
its failure
• Epoxy coating not
compatible with CP
due electrical
discontinuity.
• Epoxy bars not
suitable for long term
protection
[4, 20,
55, 59–61]
Concrete
Coating
• Applied on
concrete surface and
acts as a
barrier between
concrete
surface and
environme
nt
• Available in
numerous formulations
• Cost- effective
• Simple
application
• Increase
concrete
resistivity
• Compatible
with CP
Max 15 years
20-50 depending on
the coating
type
• Not suitable for
heavily contaminated
concrete
• Do not remove
already present
contamination in case of carbonation
• Hydrophobic
Impregnation are not suitable for standing
work and water
• Should be defect free
• Failure difficult to
measure as can occur
in different areas
[10, 59,
63]
34
Cathodic
Protection (CP)/ Cathodic
Prevention
(CPre)
• Applied to
new or old
structures
affected by chlorides.
• Also
effective in carbonated
concrete
• For ICCP, low
current density
required: CP-
5-20 mA/m2; CPre- 1-2
mA/m2
• ICCP lasts for
20-50 years or
more
• Minimal effects
on concrete
• Adequacy can
easily be
checked through
monitoring
Depends upon anode type (refer
Table 3)
• Approx.
500 £/m2
• Depends
upon
anode
• Installation
cost is
higher, however
economical
long term cost
• Permanent Technique
• ICCP requires
permanent power supply
• Require regular
maintenance and
monitoring
• The effect of
permanent anodes
needs to be
considered at the design stage
• CP not advisable for
prestressed structures
• ICCP system can
cause Stray current
corrosion
[9, 10, 32, 59,
67, 95]
Electrochemical
chloride removal
Applied to structures
in which
corrosion has not
already
initiated.
• Less intrusive-
power supply and anodes
required
temporarily
• No long-term
effect on appearance
• Increase
passivation of
reinforcing
steel
• Increase pH of
concrete.
• Completed
within 6-8
weeks
• No further
maintenance required
• Temporary
Technique
(polarization
period: 2-6 weeks)
Depends on
environmental conditions, like
shorter life in
high chloride environment and
may require to
install again
• Approx.
500 £/m2
• Depends
upon
anode
• May
require to
operate again in
future
which increases
cost
• Requires charge of 50
to 500 times
compared to CP i.e.
up to 1-2 A/m2
• Structures should use
conventional reinforcement
• Remaining service life
must be 5 to 10 years
• Length of treatment
can create logistical problems
• Initial cost higher than
CP
• Additional monitoring
is required to ensure that protection is
maintained
• Can affect concrete
• Potentially serious
effects if electrical
continuity of all steel
is not established
• Only effective in
cover zone of concrete
• Not recommended to
use with prestressed wires and risk of
alkali aggregate
reaction
[9, 10, 26, 29,
32, 59,
95]
Electrochemical Realkalization
• Applied to
structures
in which
corrosion has not
already
initiated.
• Only for
carbonated
concrete
• Less intrusive-
power supply
and anodes required
temporarily
• No long-term
effect on
appearance
• No further
maintenance
required
• Temporary
technique (polarization
period: 3-10
days)
Rarely applied as chance of
carbonated
concrete is far less as compared
to chlorinated
concrete
• Approx.
500 £/m2
• Depends
upon anode
• May
require to
operate
again in future
which
increases cost
• Requires charge of 50
to 500 times
compared to CP i.e. up to 0.5-1 A/m2
• Limited life of
treatment
• Initial cost higher than
CP
• Can affect concrete
• Potentially serious
effects if electrical
continuity of all steel is not established
• Carbonation must be
confirmed as
corrosion cause before
treatment
• Not recommended to
use with prestressed wires and risk of
alkali aggregate
reaction
[9, 10,
28, 32,
86, 95]
Note: - Cost of access and traffic management are not included, which in turn effects the economic benefits of different repair
techniques.
35
Fig. 2 Corrosion reaction mechanism adopted from [1]
Fig. 1 Schematics of corrosion process in concrete
36
Fig. 3 Schematic diagram of steel anodic behaviour in concrete chlorides presence [55]
Fig. 4 Potential –pH zone for Hydrogen Embrittlement [10]
37
Fig. 5 Pourbaix diagram for iron in chloride solution [15]
Fig. 6 Evan's diagram showing corrosion process kinetics adopted from [1]
38
(a)
(b)
(c)
Fig. 7 Corrosion protection mechanism for (a) Anodic (b) Cathodic (c) Mixed Inhibitor, adopted from [1]
39
Fig. 8 Schematic of Sacrificial Anodic Cathodic Protection System
Fig. 9 Schematic of Impressed Current Cathodic Protection System
Fig. 10 Schematic of Electrochemical Realkalization
40
Fig. 11 Schematic of Electrochemical Chloride Removal
41
5 References
1. Popov: Corrosion Engineering: Principles and Solved Problems. Elservier, Oxford (2015)
2. Michel, A., Otieno, M., Stang, H., Geiker, M.R.: Propagation of steel corrosion in concrete: Experimental and
numerical investigations. Cem. Concr. Compos. 70, 171–182 (2016). doi:10.1016/j.cemconcomp.2016.04.007
3. Razaqpur, A.G., Isgor, O.B.: Prediction of reinforcement corrosion in concrete structures. Front. Technol.
Infrastructures Eng. Struct. Infrastructures. 4, 45–69 (2009)
4. Cicek, V.: Corrosion Engineering and Cathodic Protection Handbook. John Wliey & Sons, Hoboken (2017)
5. Barnes, P., Bensted, J. eds: Structure and Performance of Cements. Presented at the (2002)
6. Berrocal, C.G., Lundgren, K., Löfgren, I.: Corrosion of steel bars embedded in fibre reinforced concrete under
chloride attack: State of the art. Cem. Concr. Res. 80, 69–85 (2016). doi:10.1016/j.cemconres.2015.10.006
7. Ebell, G., Burkert, A., Fischer, J., Lehmann, J., Müller, T., Meinel, D., Paetsch, O.: Investigation of chloride-induced
pitting corrosion of steel in concrete with innovative methods. Mater. Corros. 67, 583–590 (2016).
doi:10.1002/maco.201608969
8. Neville, A.: Chloride attack of reinforced concrete: an overview. Mater. Struct. 28, 63–70 (1995).
doi:10.1007/BF02473172
9. Broomfield, J.P.: Corrosion of Steel in Concrete: Understanding, Investigation and Repair, Second Edition. Taylor
and Francis, London and New York (2006)
10. Bertolini, L., Elsener, B., Pedeferri, P., Polder, R.: Corrosion of Steel in Concrete Prevention, Diagnosis, Repair.
Wiley VCH Verlag GmbH & Co. KGaA, Federal Republic of Germany (2004)
11. Ahmad, S.: Reinforcement corrosion in concrete structures, its monitoring and service life prediction - A review.
Cem. Concr. Compos. 25, 459–471 (2003). doi:10.1016/S0958-9465(02)00086-0
12. Angst, U., Elsener, B., Larsen, C.K., Vennesland, Ø.: Critical chloride content in reinforced concrete - A review.
Cem. Concr. Res. 39, 1122–1138 (2009). doi:10.1016/j.cemconres.2009.08.006
13. British Standards Institution: Products and systems for the protection and repair of concrete structures - Definitions,
requirements, quality control and evaluation of conformity. Br. Stand. Inst. 1504–9, (2008).
doi:10.1017/CBO9781107415324.004
14. Ann, K.Y., Song, H.W.: Chloride threshold level for corrosion of steel in concrete. Corros. Sci. 49, 4113–4133 (2007).
doi:10.1016/j.corsci.2007.05.007
15. Alonso, C., Andrade, C., Castellote, M., Castro, P.: Chloride threshold values to depassivate reinforcing bars
embedded in a standardized OPC mortar. Cem. Concr. Res. 30, 1047–1055 (2000). doi:10.1016/S0008-
8846(00)00265-9
16. Figueira, R.B., Sadovski, A., Melo, A.P., Pereira, E. V.: Chloride threshold value to initiate reinforcement corrosion
in simulated concrete pore solutions: The influence of surface finishing and pH. Constr. Build. Mater. 141, 183–200
(2017). doi:10.1016/j.conbuildmat.2017.03.004
17. Bamforth, P..: Enhancing Reinforced Concrete Durability: Guidance on selecting measures for minimising the risk
of corrosion of reinforcement in concrete. Concr. Soc. Tech. Rep. 61, (2004)
18. Nóvoa, X.R.: Electrochemical aspects of the steel-concrete system. A review. J. Solid State Electrochem. 20, 2113–
2125 (2016). doi:10.1007/s10008-016-3238-z
19. Aperador, W., Bautista-Ruiz, J., Chunga, K.: Determination of the efficiency of cathodic protection applied to
alternative concrete subjected to carbonation and chloride attack. Int. J. Electrochem. Sci. 10, 7073–7082 (2015)
20. Poursaee, A., Contributor, P.: Corrosion of Steel in Concrete Structures. Elservier Science, London (2016)
21. NACE: Stray-Current-Induced Corrosion in Reinforced and Prestressed Concrete Structures. NACE Int. 1–34 (2010)
22. British Standards Institution: Protection against corrosion by stray current from direct current systems. Br. Stand.
Inst. (2004)
42
23. Frankel, G.S.: Fundamentals of Corrosion Kinetics. In: Active Protective Coatings. pp. 17–32 (2016)
24. Burkan Isgor, O.: Modeling corrosion of steel in concrete. Corros. Steel Concr. Struct. 249–267 (2016).
doi:10.1016/B978-1-78242-381-2.00013-4
25. Glass, G.K., Buenfeld, N.R.: Chloride-induced corrosion of steel in concrete. Prog. Struct. Eng. Mater. 2, 448–458
(2000). doi:10.1002/pse.54
26. Huang, J., Wang, A.: Effective Chloride Removal in Reinforced Concrete Using Electrochemical Method in the
Presence of Calcium Nitrite. Int. J. Electrochem. Sci. 11, 4667–4674 (2016). doi:10.20964/2016.06.53
27. Geiker, M.R., Polder, R.B.: Experimental support for new electro active repair method for reinforced concrete. Mater.
Corros. 67, 600–606 (2016). doi:10.1002/maco.201608942
28. Redaelli, E., Bertolini, L.: Electrochemical repair techniques in carbonated concrete. Part I: Electrochemical
realkalisation. J. Appl. Electrochem. 41, 817–827 (2011). doi:10.1007/s10800-011-0301-4
29. Elsener, B., Angst, U.: Mechanism of electrochemical chloride removal. Corros. Sci. 49, 4504–4522 (2007).
doi:10.1016/j.corsci.2007.05.019
30. Polder, R.B., Peelen, W.H.A., Stoop, B.T.J., Neeft, E.A.C.: Early stage beneficial effects of cathodic protection in
concrete structures. Mater. Corros. 62, 105–110 (2011). doi:10.1002/maco.201005803
31. Broomfield, J.: Anode Selection for Protection of Reinforced Concrete Structures. Mater. Perform. 46, (2007)
32. Drewett, J., Broomfield, J.: An Introduction to Electrochemical Rehabilitation Techniques - Technical Note 2. CPA
Tech. NOTE. (2011)
33. Raja, P.B., Ismail, M., Ghoreishiamiri, S., Mirza, J., Ismail, M.C., Kakooei, S., Rahim, A.A.: Reviews on Corrosion
Inhibitors: A Short View. Chem. Eng. Commun. 203, 1145–1156 (2016). doi:10.1080/00986445.2016.1172485
34. Atkins, C., Merola, R., Foster, A.: Corrosion inhibitors. CPA Tech. NOTE. 16, 13–15 (2010)
35. Söylev, T.A., Richardson, M.G.: Corrosion inhibitors for steel in concrete: State-of-the-art report. Constr. Build.
Mater. 22, 609–622 (2008). doi:10.1016/j.conbuildmat.2006.10.013
36. ACI Committee 222: Protection of Metals in Concrete Against Corrosion. ACI 222R-01. 1–41 (2001)
37. Lee, H.-S., Saraswathy, V., Kwon, S.-J., Karthick, S.: Corrosion Inhibitors for Reinforced Concrete: A Review.
Corros. Inhib. Princ. Recent Appl. (2018). doi:10.5772/intechopen.72572
38. Shen, M., Hansen, A.: Protecting Concrete Reinforcement Using Admixtures with Migratory Corrosion Inhibitors
and Water Repellent Component. NACE Corros. 4250, 1–7 (2014)
39. Malik, A.U., Andijani, I., Al-Moaili, F., Ozair, G.: Studies on the performance of migratory corrosion inhibitors in
protection of rebar concrete in Gulf seawater environment. Cem. Concr. Compos. 26, 235–242 (2004).
doi:10.1016/S0958-9465(03)00042-8
40. Bavarian, B., Reiner, L., Kim, C.Y.: Corrosion Protection of Steel Rebar in Concrete By Migrating Corrosion
Inhibitors. NACE Corros. 1–10 (2003)
41. Pei, X., Noël, M., Green, M., Fam, A., Shier, G.: Cementitious coatings for improved corrosion resistance of steel
reinforcement. Surf. Coatings Technol. 315, 188–195 (2017). doi:10.1016/j.surfcoat.2017.02.036
42. Gece, G.: Drugs: A review of promising novel corrosion inhibitors. Corros. Sci. 53, 3873–3898 (2011).
doi:10.1016/j.corsci.2011.08.006
43. Raja, P.B., Sethuraman, M.G.: Natural products as corrosion inhibitor for metals in corrosive media - A review.
Mater. Lett. 62, 113–116 (2008). doi:10.1016/j.matlet.2007.04.079
44. Etteyeb, N., Nóvoa, X.R.: Inhibition effect of some trees cultivated in arid regions against the corrosion of steel
reinforcement in alkaline chloride solution. Corros. Sci. (2016). doi:10.1016/j.corsci.2016.07.016
45. The Concrete Society: Guidance on the use of stainless steel reinforcement. Concr. Soc. TR 51, (1998)
46. Moser, R.D., Singh, P.M., Kahn, L.F., Kurtis, K.E.: Chloride-induced corrosion resistance of high-strength stainless
steels in simulated alkaline and carbonated concrete pore solutions. Corros. Sci. 57, 241–253 (2012).
43
doi:10.1016/j.corsci.2011.12.012
47. Serdar, M., Žulj, L.V., Bjegović, D.: Long-term corrosion behaviour of stainless reinforcing steel in mortar exposed
to chloride environment. Corros. Sci. 69, 149–157 (2013). doi:10.1016/j.corsci.2012.11.035
48. Qian, S., Qu, D., Coates, G.: Galvanic Coupling Between Carbon Steel and Stainless Steel Reinforcements. Can.
Metall. Q. 45, 475–483 (2006). doi:10.1179/cmq.2006.45.4.475
49. British Standards Institution: Cathodic Protection of Submarine Pipelines by Galvanic Anodes. Br. Stand. Inst. 12474,
(2001)
50. ACI Committee 440: Report on Fiber-Reinforced Polymer (FRP) Reinforcement for Concrete Structures. ACI Comm.
440. 440R, (2007)
51. Waldron, P; Byars, E.A.; Dejke, V.: Durability of FRP in Concrete A State of the Art. Compos. Constr. 92–101 (2001)
52. Suh, K., Mullins, G., Sen, R., Winters, D.: Effectiveness of fiber-reinforced polymer in reducing corrosion in marine
environment. ACI Struct. J. 104, 76–83 (2007)
53. ACI Committee 440: Guide for the design and construction of externally bonded FRP systems for strengthening
existing structures. ACI Comm. 440. 440.2R, (2008)
54. Wu, G., Dong, Z.-Q., Wang, X., Zhu, Y., Wu, Z.-S.: Prediction of Long-Term Performance and Durability of BFRP
Bars under the Combined Effect of Sustained Load and Corrosive Solutions. J. Compos. Constr. 1–9 (2014).
doi:10.1061/(ASCE)CC.1943-5614.0000517.
55. Kumar, V.: Protection of steel reinforcement for concrete - A review. Corros. Rev. 16, 317–358 (1998)
56. Revie, R.W., Uhlig, H.H.: Corrosion and Corrosion Control: An Introduction to Corrosion Science and Engineering.
John Wliey & Sons, New Jersey (2008)
57. Pugazhenthy, L.: Galvanized Rebars in RCC Structures – Economic & Technical Advantages. CORCON. 16–19
(2016)
58. Bellezze, T., Timofeeva, D., Giuliani, G., Roventi, G.: Effect of soluble inhibitors on the corrosion behaviour of
galvanized steel in fresh concrete. Cem. Concr. Res. 107, 1–10 (2018). doi:10.1016/j.cemconres.2018.02.008
59. Yehia, S., Host, J.: Conductive concrete for cathodic protection of bridge decks. ACI Mater. J. 107, 577–585 (2010)
60. Mohammed, H.S., Knight, G.M.S.: Influence of Coating Damage on Performance of Coated Rebars under
Accelerated Corrosion Conditions. In: CORCON (2016)
61. Pour-Ali, S., Dehghanian, C., Kosari, A.: Corrosion protection of the reinforcing steels in chloride-laden concrete
environment through epoxy/polyaniline-camphorsulfonate nanocomposite coating. Corros. Sci. 90, 239–247 (2015).
doi:10.1016/j.corsci.2014.10.015
62. Pei, X., Noël, M., Green, M., Fam, A., Shier, G.: Cementitious coatings for improved corrosion resistance of steel
reinforcement. Surf. Coatings Technol. 315, 188–195 (2017). doi:10.1016/j.surfcoat.2017.02.036
63. Lambert, P., MacDonald, M.: Coating Concrete. CPA Tech. NOTE. 18, (2010)
64. Jiesheng, L., Xiaoqiang, G., Faping, L., Xiang, H., Rongtang, Z.: The Science Behind It : Effects of Silane Additives
on Corrosion Resistance and Durability of Mortar, (2018)
65. Pan, X., Shi, Z., Shi, C., Ling, T.C., Li, N.: A review on concrete surface treatment Part I: Types and mechanisms.
Constr. Build. Mater. 132, 578–590 (2017). doi:10.1016/j.conbuildmat.2016.12.025
66. Goyal, A., Ganjian, E., Pouya, H.S.: BOND STRENGTH BEHAVIOUR OF ZINC RICH PAINT COATING ON
CONCRETE SURFACE. In: Young Researchers’ Forum IV Innovation in Construction Materials. pp. 21–25. ,
Newcastle (2018)
67. Byrne, A., Holmes, N., Norton, B.: State-of-the-art review of cathodic protection for reinforced concrete structures.
Mag. Concr. Res. 68, 1–14 (2016). doi:10.1680/jmacr.15.00083
68. Pedeferri, P.: Cathodic protection and cathodic prevention. Constr. Build. Mater. 10, 391–402 (1996).
doi:10.1016/0950-0618(95)00017-8
44
69. US Federal Highway Administration: Long-term effectiveness of cathodic protection systems on highway structures.
Publ. No. FHWA-RD-01-096, FHWA. (2001)
70. Bertolini, L., Bolzoni, F., Pedeferri, P., Lazzari, L., Pastore, T.: Cathodic protection and cathodic prevention in
concrete: principles and applications*. J. Appl. Electrochem. 28, 1321–1331 (1998)
71. Preston, J.: Cathodic Protection for New Structures Technical note 23.
72. Darowicki, K., Orlikowski, J., Cebulski, S., Krakowiak, S.: Conducting coatings as anodes in cathodic protection.
Prog. Org. Coatings. 46, 191–196 (2003). doi:10.1016/S0300-9440(03)00003-1
73. NACE International: Sacrificial Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Concrete
Structures. NACE. SP0216, (2016)
74. Lasa, I.R., Islam, M., Duncan, M.: Galvanic Cathodic Protection for High Resistance Concrete in Marine
Environments. 1–13 (2017)
75. Nikolakakos, S.: Cathodic Protection System Design for Steel Pilings of a Wharf Structure Reference: Am. Soc. Test.
Mater. (1999)
76. BS7361-1: Cathodic Protection Part 1: Code of practice for land and marine applications. Br. Stand. (1991).
doi:10.4028/www.scientific.net/KEM.35-36.301
77. Leng, D.L.: Cathodic Protection on steel reinforced concrete marine structures. NACE Corros. 3–4 (2017)
78. Parthiban, G.T., Parthiban, T., Ravi, R., Saraswathy, V., Palaniswamy, N., Sivan, V.: Cathodic protection of steel in
concrete using magnesium alloy anode. Corros. Sci. (2008). doi:10.1016/j.corsci.2008.08.040
79. Wilson, K., Jawed, M., Ngala, V.: The selection and use of cathodic protection systems for the repair of reinforced
concrete structures. In: Construction and Building Materials (2013)
80. Society, T.C.: Cathodic Protection of Stee Concrete. (2011)
81. Koleva, D.A., de Wit, J.H.W., van Breugel, K., Lodhi, Z.F., Ye, G.: Investigation of Corrosion and Cathodic
Protection in Reinforced Concrete. J. Electrochem. Soc. 154, C261 (2007). doi:10.1149/1.2715313
82. NACE: Impressed Current Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Concrete Structures.
NACE Int. SP0290, (2007)
83. Polder, R.B., Worm, D., Courage, W., Leegwater, G.: Performance and working life of cathodic protection systems
for concrete structures. In: Grantham, M., Mechtcherine, V., and Schneck, U. (eds.) CONCRETE SOLUTIONS, 4TH
INTERNATIONAL CONFERENCE ON CONCRETE REPAIR. pp. 157–162. CRC Press, DRESDEN, GERMANY
(2011)
84. The Concrete Society: Cathodic protection of steel in concrete- Appendices. The Concrete Society (2011)
85. Glass, G.K., Roberts, a. C., Davison, N.: Hybrid corrosion protection of chloride-contaminated concrete. Proc. ICE
- Constr. Mater. 161, 163–172 (2008). doi:10.1680/coma.2008.161.4.163
86. Broomfield, J.P.: Electrochemical Realkalisation of Steel Reinforced Concrete - A State of the Art Report. (2004)
87. Marques, P.F., Costa, A.: Service life of RC structures : Carbonation induced corrosion . Prescriptive vs .
performance-based methodologies. Constr. Build. Mater. 24, 258–265 (2010).
doi:10.1016/j.conbuildmat.2009.08.039
88. British Standards Institution: Electrochemical realkalization and chloride extraction treatments for reinforced
concrete. Br. Stand. Inst. 14038–1, (2016)
89. NACE: Electrochemical Realkalization and Chloride Extraction for Reinforced Concrete. NACE Int. SP0107, 1–24
(2017)
90. Ribeiro, P.H.L.C., Meira, G.R., Ferreira, P.R.R., Perazzo, N.: Electrochemical realkalisation of carbonated concretes
– Influence of material characteristics and thickness of concrete reinforcement cover. Constr. Build. Mater. 40, 280–
290 (2013). doi:10.1016/j.conbuildmat.2012.09.076
91. Yeih, W., Chang, J.J.: A study on the efficiency of electrochemical realkalisation of carbonated concrete. Constr.
Build. Mater. 19, 516–524 (2005). doi:10.1016/j.conbuildmat.2005.01.006
45
92. British Standards Institution: Electrochemical realkalization and chloride extraction treatments for reinforced
concrete. Part 2: Chloride extraction. Br. Stand. Inst. 14038–2, (2011)
93. Sánchez, M., Alonso, M.C.: Electrochemical chloride removal in reinforced concrete structures: Improvement of
effectiveness by simultaneous migration of calcium nitrite. Constr. Build. Mater. 25, 873–878 (2011).
doi:10.1016/j.conbuildmat.2010.06.099
94. Broomfield, J.P.: The Principles and Practice of Galvanic Cathodic Protection for Reinforced Concrete Structures-
Technical Notes 6. CPA Tech. NOTE. (2007)
95. Martínez, I., Andrade, C., Castellote, M., de Viedma, G.P.: Advancements in non-destructive control of efficiency of
electrochemical repair techniques. Corros. Eng. Sci. Technol. 44, 108–118 (2009). doi:10.1179/174327808X286266
top related